Staphylococcal enterotoxins (SEs) A through E are the most common cause of food poisoning [Bergdoll, M. S. (1983) In Easom CSF, Aslam C., eds. Staphylococci and staphylococcal infections. London: Academic Press, pp 559-598] and are associated with several serious diseases [Schlievert, P. M. (1993) J. Infect. Dis. 167: 997-1002; Ulrich et al. (1995) Trends Microbiol. 3: 463-468], such as bacterial arthritis [Schwab et al. (1993) J. Immunol. 150; 4151-4159; Goldenberg et al. (1985) N. Engl. J. Med. 312: 764-771], other autoimmune disorders [Psnett, D. N. (1993) Semin. Immunol. 5: 65-72], and toxic shock syndrome [Schlieverst, P. M. (1986) Lancet 1: 1149-1150; Bohach et al. (1990) Crit. Rev. Microbiol. 17: 251-272]. The nonenterotoxic staphylococcal superantigen toxic shock syndrome toxin-1 (TSST-1) was first identified as a causative agent of menstrual-associated toxic shock syndrome [Schlievert et al. (1981) J. Infect. Dis. 143: 509-516]. Superantigen-producing Staphylococcus aureus strains are also linked to Kawasaki syndrome, an inflammatory disease of children [Leung et al. (1993) Lancet 342: 1385-1388].
The staphylococcal enterotoxins A-E, toxic shock syndrome toxin-1 (TSST-1), and streptococcal pyrogenic exotoxins A-C are soluble 23-29-kD proteins commonly referred to as bacterial superantigens (SAgs). Bacterial superantigens are ligands for both major histocompatibility complex (MHC) class II molecules, expressed on antigen-presenting cells, and the variable portion of the T cell antigen receptor xcex2 chain (TCR Vxcex2) [Choi et al. (1989) Proc. Natl. Acad. Sci. USA 86:8941-8945; Fraser, J. D. (1989) Nature 339:221-223; Marrack et al. (1990) Science 248: 705-711; Herman et al. (1991) Annu. Rev. Immunol. 9: 745-772; Mollick et al. (1989) Science 244:817-820].
Each bacterial superantigen has a distinct affinity to a set of TCR Vxcex2, and coligation of the MHC class II molecule polyclonally stimulates T cells [White et al. (1989) Cell 56: 27-35; Kappler et al. (1989) Science 244: 811-813; Takimoto et al. (1990) Eur J. Immunol. 140: 617-621]. Pathologically elevated levels of cytokines that are produced by activated T cells are the probable cause of toxic shock symptoms [Calson et al. (1985) Cell. Immunol. 96: 175-183; Stiles et al. (1993) Infect. Immun. 61: 5333-5338]. In addition, susceptibility to lethal gram-negative endotoxin shock is enhanced by several bacterial superantigens [Stiles, et al., supra]. Although antibodies reactive with superantigens are present at low levels in human sera [Takei et al. (1993) J. Clin. Invest. 91: 602-607], boosting antibody titers by specific immunization may be efficacious for patients at risk for toxic shock syndrome and the other disorders of common etiology.
A vaccine approach to controlling bacterial superantigen-associated diseases presents a unique set of challenges. Acute exposure to bacterial superantigens produces T cell anergy, a state of specific non-responsiveness [Kawabe et al. (1991) Nature 349: 245-248], yet T cell help is presumably a requirement for mounting an antibody response.
Presently, the only superantigen vaccines available are chemically inactivated toxoids from different bacteria which have several disadvantages. The chemical inactivation process can be variable for each production lot making the product difficult to characterize. The chemical used for inactivation, (e.g. formaldehyde), is often toxic and does not negate the possibility of reversion of the inactivated superantigen to an active form. In addition, the yields of wild-type toxin from bacterial strains used for making toxoids are often low.
The present invention relates to a vaccine which overcomes the disadvantages of the chemically inactivated toxoids described above. The superantigen vaccine(s) of the present invention is/are designed to protect individuals against the pathologies resulting from exposure to one or several related staphylococcal and streptococcal toxins. The superantigen vaccine is comprised of a purified protein product that is genetically attenuated by DNA methodologies such that superantigen attributes are absent, however the superantigen is effectively recognized by the immune system and an appropriate antibody response is produced.
Specifically, the vaccine of the present invention is a product of site-directed mutagenesis of the DNA coding sequences of superantigen toxins resulting in a disruption of binding to both the MHC class II receptor and to the T-cell antigen receptor. A comprehensive study of the relationships of the superantigen structures of TSST-1, streptococcal pyrogenic exotoxin-A (SPEa), staphylococcal enterotoxin B (SEB), and staphylococcal enterotoxin A, to receptor binding were undertaken to provide insight into the design of the vaccine. From these studies, critical amino acid residues of the toxin responsible for binding the superantigen to the human MHC receptor were defined. Site-directed mutagenesis of the gene encoding the toxin and expression of the new protein product resulted in a superantigen toxin with disrupted binding to the MHC receptors.
Therefore, it is an object of the present invention to provide a superantigen toxin DNA fragment which has been genetically altered such that binding of the encoded altered toxin to the MHC class II or T-cell antigen receptor is disrupted. Such a DNA fragment is useful in the production of a vaccine against superantigen toxin infections.
It is another object of the present invention to provide a superantigen toxin amino acid sequence which has been altered such that the binding of the encoded altered toxin to the MHC class II or T-cell antigen receptor is disrupted. Such a sequence is useful for the production of a superantigen toxin vaccine.
It is another object of the invention to provide a recombinant vector comprising a vector and the DNA fragment described above.
It is a further object of the present invention to provide host cells transformed with the above-described recombinant DNA constructs. Host cells include cells of other prokaryotic species or eukaryotic plant or animal species, including yeasts, fungi, plant culture, mammalian and nonmammalian cell lines, insect cells and transgenic plants or animals.
It is another object of the present invention to provide a method for producing altered superantigen toxin with disrupted MHC class II and T-cell antigen receptor binding which comprises culturing a host cell under conditions such that a recombinant vector comprising a vector and the DNA fragment described above is expressed and altered superantigen toxin is thereby produced, and isolating superantigen toxin for use as a vaccine against superantigen toxin-associated bacterial infections and as a diagnostic reagent.
It is still another object of the invention to provide a purified altered superantigen toxin useful as a vaccine and as a diagnostic agent.
It is another object of the invention to provide a purified altered superantigen toxin for the therapeutic stimulation of, or other in vivo manipulation of, selective T cell subsets, or ex vivo manipulation of T cells for in vivo therapeutic purposes in mammals. Diseases, such as autoimmunity, wherein T-cell responses of limited diversity (oligoclonal) are evident. Altered superantigens may be used to therapeutically inactivate (induce anergy in) T cells in diseases wherein oligoclonal T-cell responses are evident such as autoimmune diseases, for example. For diseases in which specific T-cell subsets are not active or are anergetic, altered superantigens may be used to therapeutically stimulate these T cells. Such disease include, but are not limited to, infectious diseases and cancers wherein specific subsets of cytotoxic or helper T cells are inactivated or are otherwise unable to respond normally to the antigenic stimulation of the disease moiety.
It is a further object of the present invention to provide an antibody to the above-described altered superantigen toxin for use as a therapeutic agent and as a diagnostic agent.
It is yet another object of the invention to provide a superantigen toxin vaccine comprising an altered superantigen toxin effective for the production of antigenic and immunogenic response resulting in the protection of an animal against superantigen toxin infection.
It is a further object of the invention to provide a multivalent superantigen toxin vaccine comprising altered toxins from a variety of streptococcal and staphylococcal toxins effective for the production of antigenic and immunogenic response resulting in the protection of an animal against infection with bacterial superantigen toxin-expressing strains and against other direct or indirect exposures to bacterial superantigen toxins such as might occur by ingestion, inhalation, injection, transdermal or other means.
It is yet another object of the present invention to provide a method for the diagnosis of superantigen toxin-associated bacterial infection comprising the steps of:
(i) contacting a sample from an individual suspected of having a superantigen toxin-associated bacterial infection with antibodies which recognize superantigen toxin using antibodies generated from the altered superantigen toxin; and
(ii) detecting the presence or absence of a superantigen-associated bacterial infection by detecting the presence or absence of a complex formed between superantigen toxin in said sample and antibodies specific therefor.
It is yet another object of the present invention to provide a method for the diagnosis of superantigen bacterial infection comprising the steps of:
(i) contacting a sample from an individual suspected of having the disease with lymphocytes which recognize superantigen toxin produced by said superantigen bacteria or lymphocytes which recognize altered superantigen toxin; and
(ii) detecting the presence or absence of responses of lymphocytes resulting from recognition of superantigen toxin. Responses can be, for example, measured cytokine release, increase of activation markers, mitotic activity, or cell lysis. The lymphocytes responding to the altered superantigen toxins recognize them as recall antigens not as superantigens, therefore the response is an indicator of prior exposure to the specific superantigen. The absence of a response may indicate no prior exposure, a defective immune response or in some cases a manifestation of T-cell anergy. Anergy is defined here as antigen-specific or a generalized non-responsiveness of subsets of T cells.
It is a further object of the present invention to provide a diagnostic kit comprising an antibody against an altered superantigen toxin and ancillary reagents suitable for use in detecting the presence of superantigen toxin in animal tissue or serum.
It is another object of the present invention to provide a detection method for detecting superantigen toxins or antibodies to superantigen toxin in samples, said method comprising employing a biosensor approach.
Such methods are known in the art and are described for example in Karlsson et al. (1991) J. Immunol. Methods 145, 229-240 and Jonsson et al. (1991) Biotechniques 11, 620-627.
It is yet another object of the present invention to provide a therapeutic method for the treatment or amelioration of symptoms of superantigen-associated bacterial infection, said method comprising providing to an individual in need of such treatment an effective amount of sera from individuals immunized with one or more altered superantigen toxins from different bacteria in a pharmaceutically acceptable excipient.
It is further another object of the present invention to provide a therapeutic method for the treatment or amelioration of symptoms of superantigen toxin-associated bacterial infection, said method comprising providing to an individual in need of such treatment an effective amount of antibodies against altered superantigen toxins in a pharmaceutically acceptable excipient.
It is another object of the present invention to provide a therapeutic method for the treatment or amelioration of symptoms of bacterial superantigen toxin infection, said method comprising providing to an individual in need of such treatment an effective amount of altered superantigen from a variety of streptococcal and staphylococcal bacteria in order to inhibit adhesion of superantigen bacterial toxin to MHC class II or T-cell receptors by competitive inhibition of these interactions.
It is yet another object of the present invention to provide a therapeutic method for the treatment of diseases that may not be associated directly with superantigen toxins but which result in specific nonresponsiveness of T-cell subsets, said method comprising the administration of altered superantigen toxins, in vivo or ex vivo, such that T-cell subsets are expanded or stimulated. Diseases which cause anergy or nonresponsiveness of T-cells include, but are not limited to, infectious diseases.
It is another object of the present invention to provide a therapeutic method for the treatment of diseases associated with expanded or over-stimulated T-cell subsets, such as autoimmunity for example, said method comprising administration of altered superantigen toxin, in vivo or ex vivo, such that anergy or inactivation of disease associated T-cells is produced. In this case, superantigen mutants can be designed with altered but not attenuated T-cell receptor binding, to cause anergy of only the select (i.e. 1-3) T-cell subsets that are pathologically activated.